Drive wheels of the type referred to above are known, for example, through U.S. Pat. No. 4,472,880 and have greatly contributed to the technical and commercial breakthrough of so called ring saws which are cutting machines having annular saw blades. This, however, does not mean that the drive of such annular saw blades has been problem-free. One such problem stems from the fact that in order for the drive between the drive wheel and the saw blade to be efficient, the bevelled surfaces that define the wedge-shaped drive-groove must bear with adequate pressure on the wedge-shaped inner edge of the saw blade. According to U.S. Pat. No. 4,472,880, this pressure is provided by causing the first annular surfaces of the annular elements to be pressed against the wedge-shaped edge of the saw blade. In practice, it has turned out that the pressure force required to provide a contact pressure sufficient for an efficient drive must be so great that it has caused severe problems, including great wear upon the saw blade, as well as of the drive wheel, which in turn has reduced the service life of these machine elements.
It is suggested in U.S. Pat. No. 4,793,065 that the wedge-shaped edge of the saw blade can be pressed in the radial direction into the drive-groove of the drive-wheel. Those parts of the drive wheel which between them define the wedge-shaped drive wheel are designed to be stationary relative to each other. This principle has turned out to give a better drive than that one which is based on pressing in the axial direction according to U.S. Pat. No. 4,472,880. However, in this case the walls of the wedge-shaped drive-groove are also subjected to heavy wear. This problem can be addressed by manufacturing the drive wheel of a more wear resistant material, but this solution can be very expensive.
According to U.S. Pat. No. 6,243,956, only a minor part of the drive wheel is made of a wear resistant material, while the rest of the drive wheel is made of conventional structural steel. The annular drive ring shown in the '956 patent, however, is difficult to manufacture, independent of the material used in its construction. The drive ring cannot, for example, because of its geometry, be manufactured through cold forging even if the material is a conventional structural steel; a feature which is desirable since cold forging is a simple manufacturing technique that can make the product cheaper. Even more difficult would the manufacturing be if the drive ring shall be made of a more qualified material. This is particularly true if it shall be made of a very wear resistant material, such as a sintered carbide material or a wear resistant ceramic material because of the difficulties in machining such materials by means of cutting tools.
Further, it is particularly difficult to establish the drive-groove, and especially the annular recess which should exist in the bottom of the wedge-shaped groove in order to prevent the wedge-shaped edge of the saw blade from reaching the bottom of the wedge-shaped groove, since that would severely impair the driving efficiency of the drive wheel and also increase the wear of the drive ring as well as of the saw blade.